Malaria cases appear to have been slashed by half in more than a third of countries battling the disease following a renewed push by the United Nations to eradicate the disease, the World Health Organization said Tuesday.

In a new global report on malaria, the UN health agency said it was cautiously optimistic the mosquito-borne disease's spread is slowing, even though its information is patchy and based largely on modelling.

'I fear the window of donor largesse for malaria may be beginning to close.'— Matthew Lynch, malaria expert

Malaria infected more than 240 million people last year and killed an estimated 863,000, mostly in Africa. Repeated attempts to eradicate the disease have flopped and until recently, the number of cases has been rising.

Last year, the United Nations started an initiative that aims to provide bed nets to protect against malaria to everyone who needs them by the end of 2010. More money has also been invested, jumping from about $730 million US in 2006 to $1.7 billion US this year.

"There is finally a bit of light at the end of this tunnel," said Paul Reiter, a malaria expert at the Pasteur Institute in Paris who was not connected to the report.

Still, much remains to be done. Despite the drop in cases, the number of infections fell the least in countries with the biggest problems, such as Nigeria and the Democratic Republic of Congo.

WHO says 80 per cent of children with a fever in malaria-endemic countries should get medicines.

According to the report, fewer than 15 per cent did. Signs of drug resistance to the malaria drugs are emerging and there are few alternatives in the pipeline.

Too early to claim success

There is also considerable uncertainty about the data on which the report is based, and the numbers all come with a big margin of error. There are discrepancies between the numbers of bed nets reported to have been distributed by authorities and those actually in use, and the numbers of cases are based on modelling, not actual numbers of people with malaria.

Some experts said it will be difficult to sustain the effort.

"I fear the window of donor largesse for malaria may be beginning to close," said Matthew Lynch, director of the Global Program on Malaria at the Johns Hopkins Bloomberg School of Public Health. "We need a lot more money and we're not even close to what we need now," he said.

WHO estimated that $5 billion is required every year to make a significant dent into malaria.

Richard Tren, director of Africa Fighting Malaria, an advocacy group based in South Africa and the U.S., said malaria-endemic countries needed to invest more into the effort themselves, instead of relying on international donors.

He questioned whether countries with growing economies like India and China should get donor aid. "Why are international taxpayers funding 50-cent malaria treatments when both those countries are rich enough to fund their own space programs?"

Tren said while the report was encouraging, it was still preliminary.

"Let's not claim success too soon," he said. "There is good news, but that doesn't mean we've made huge strides in solving the problem."